In conventional encoded data transmission technologies, various types of cables are used for achieving noise-resistant transmission. Of such various cables, coaxial cables capable of preventing noise by shielding a signal line are generally used. However, the coaxial cables have problems of requiring high shielding cost and heavy cable weight.
One technology known to solve the above problems is a differential transmission technology using a twist pair cable. In this technology, with a differential receiver removing in-phase components, it is possible to achieve a high anti-noise capability. Furthermore, when a twist pair cable is used, shielding is not required, unlike the case of the coaxial cable. Thus, cost reduction and light-weight design can be advantageously achieved.
The twist pair cable is used for transmission with two lines. Therefore, a signal inherently has a polarity. For this reason, as for a conventional connector used for the twist pair cable, a correct inserting orientation and the polarity of the cable to be connected are predetermined. Therefore, when a user erroneously connects the connector with its inserting orientation (the polarity of the connector) reversed or when a cable of reversed connection is used, a signal with its polarity reversed is received by a device. In this case, data cannot be correctly received.
In one case, a connection is achieved so as not to make a connector with an incorrect polarity of the cable (so as not to make a cable and a connector reversed in polarity between a transmission side and a reception side). In this case, however, the cable and the connector have to be made in consideration of the polarities at the transmission side and the reception side (so that the polarity at the transmission side always coincides with that at the reception side). Therefore, it requires time and cost to manufacture the cable and the connector.
Therefore, an object of the present invention is to provide a data transmission system in which normal transmission can be performed regardless of the polarity of the cable.